Study of glasses/glass-ceramics in the SrO-ZnO-SiO2 system as high temperature sealant for SOFC applications

Glasses having composition (in wt.%) 51SrO-9ZnO-(40−x)SiO₂ (SZS), where x represents the additives like B₂O₃, Al₂O₃, V₂O₅, and Cr₂O₃, were prepared by melt-quench method and transformed into glass-ceramics by controlled crystallization based on differential thermal analysis (DTA) data. Glasses and glass-ceramics were characterized using dilatometry, X-ray diffraction (XRD), microhardness, and Raman spectroscopy. XRD revealed that glass-ceramics are composed of mainly Sr₂ZnSi₂O₇ and SrSiO₃ crystalline phases along with residual glassy phase. Raman spectroscopy showed that main constitutes of the glass network are the Q¹ and Q² silicate structural units. With the addition of B₂O₃ and other additives silicate glass network depolymerizes and concentration of Q¹ structural units increases at the expense of Q² units. Formation of phases during crystallization depends on the presence of different silicate structural units in the glass matrix. B₂O₃ goes into the glass network as triangular (BO₃) borate structural units and at higher concentration of B₂O₃, only a part of the B₂O₃ forms tetragonal (BO₄) structural units. Investigated glasses and glass-ceramics have thermal expansion coefficient (TEC) in the range of 105-120 × 10⁻⁷/°C which matches with TEC of other cell components. B₂O₃ containing SZS glasses show good adhesion/bonding with YSZ and Crofer 22 APU. Elemental line scans indicate that interdiffusion of Fe, Cr and Si across interface is responsible for good bonding with Crofer 22 APU and interdiffusion of Sr, Si, Y and Zr is responsible for good bonding with YSZ.